A seat belt system for restraining an occupant of a vehicle ordinarily includes seat belt webbing, a seat belt buckle and a seat belt retractor. A locking tongue is connected to the webbing and is releasably lockable in the buckle when the webbing is extended around the vehicle occupant. The retractor includes a spool upon which the webbing is wound. The spool rotates in an unwinding direction when the vehicle occupant extracts the webbing from the retractor and moves the webbing toward the extended position in which the tongue is locked in the buckle. When the tongue is subsequently unlocked and released from the buckle, a rewind spring in the retractor rotates the spool in a winding direction to retract the webbing back into the retractor.
When the vehicle experiences a collision, the vehicle decelerates and the vehicle occupant wearing the seat belt webbing moves forcefully against the webbing. The force which is then applied to the webbing by the vehicle occupant urges the webbing to move outward from the retractor. Therefore, the retractor includes a locking mechanism which operates to block rotation of the spool in the unwinding direction. The locking mechanism thus operates to prevent the webbing from being further extracted from the retractor when the vehicle experiences a collision.
In some seat belt systems, the webbing is prevented from being further extracted from the retractor throughout the time that the webbing is secured around the vehicle occupant, i.e., the webbing is maintained in a cinched condition. For example, some child seat belt systems maintain the webbing in a cinched condition.